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[Super 14]N quadrupolar couplings for eight different polypeptide samples, each of whose secondary structure ([alpha]-helix or [beta]-sheet) is known are examined to establish a relationship between the secondary structure of a peptide and the quadrupolar coupling of its amide [super 14]N. Gaussian03 ab initio calculations revealed that the quadrupolar coupling for the [alpha]-helix is larger than that for the [beta]-sheet by a few 100 kHz irrespective of the kind of amino acid residues examined (Ala, Val, Leu).

To establish a relationship between the secondary structure of a peptide and the quadrupolar coupling of its amide 14N, we examined 14N quadrupolar couplings for eight different polypeptide samples, each of whose secondary structure (α-helix or β-sheet) is known. The 14N quadrupolar coupling is estimated from indirect observation of a 14N overtone resonance under magic-angle spinning. From the observed indirect 14N overtone spectra and calculated 14N quadrupolar couplings for model molecules by using ab initio calculation (Gaussiano3), it is shown that the quadrupolar coupling for the α-helix is larger than that for the β-sheet by a few 100 kHz irrespective of the kind of amino acid residues examined (Ala, Val, Leu). [ABSTRACT FROM AUTHOR]